A piece of heavy equipment, such as earthmoving equipment, is often operated in very adverse conditions, including dust or mud, extreme temperatures, high winds, etc. A heating, ventilating, and air conditioning (HVAC) unit must both operate in these conditions and protect itself from the hazards posed by these conditions.
However, diagnosis of problems such as clogged fans or low levels of refrigerant is difficult and the inability to diagnose such problems creates a risk of severe damage to expensive HVAC components such as the compressor.
U.S. Pat. No. 5,289,692 (the '692 patent) describes a heat transfer system that controls operation of a compressor, expansion valve, and whether a compressor fan is off or on based on the working fluid quality and high side fluid pressure. The '692 patent does not contemplate continuous control of the compressor fan speed while in a normal operating range or reversing the fan when the pressure increases beyond a limit.